The present application is a national stage application of the PCT application Ser. No. PCT/GB98/00525 filed Mar. 10, 1998, which claims priority to the Great Britain Patent Application No. 9705182.5 filed Mar. 13, 1997.
The present invention relates to an improved method for cleaning a pipeline, in particular a gas main, and to an improved apparatus for carrying out the method.
Gas mains can contain a substantial amount of debris, for example light dust through to heavy scale, or foreign bodies and other intruding material. This material needs to be removed in particular before any internal inspection or repair is carried out and because it reduces the carrying capacity of the main.
It is known to clean gas mains in a decommissioned state. but this has the disadvantage that the gas supply to the customers supplied by that main has to be interrupted while the cleaning is being carried out, thus causing inconvenience and difficulties to these customers.
It is an object of the present invention to provide a method of cleaning a pipeline, in particular a gas main in which the above disadvantages are reduced or substantially obviated. It is a further object of the present invention to provide an apparatuis for carrying out the cleaning method.
The present invention provides a method of cleaning a pipeline for transporting a fluid, in particular a gas, more particularly a gas which forms an explosive mixture when mixed with air, which method comprises removing debris from the pipeline by means of a collecting device and a removal unit, characterised in that the pipeline is cleaned in a commissioned state, without interrupting the flow of fluid through the pipeline, by removing a mixture of fluid and debris from the pipeline by means of suction, separating the debris from the fluid and re-injecting the cleaned fluid into the pipeline.
In particular, the present invention provides a method of cleaning a pipeline for transporting a fluid, in particular a gas, more particularly a gas which forms an explosive mixture when mixed with air, which method comprises the steps of
(i) inserting into the pipeline to be cleaned a device for scraping the internal wall of the pipe and collecting the debris deposited by this scraping, together with loose debris in the pipe;
(ii) propelling the collecting device, together with the collected debris, along the pipeline to a collection point;
(iii) introducing a removal unit in the pipeline for location close to the collecting point and
(iv) removing debris from the pipeline by means of this removal unit
characterised in that the pipeline is cleaned in a commissioned state, without interrupting the flow of fluid through the-pipeline, and the removal unit comprises a suction head which is powered by a vacuum unit located in a cleaning unit, which cleaning unit is connected to the pipeline to be cleaned at a first point, close to the collection point for debris, and at a second point downstream (with respect to the direction of fluid flow) of the first point, and a mixture of gas and debris is removed by suction from the pipeline at the first point, passed through the cleaning unit, the debris is separated out from the gas/debris mixture as it is passed through the cleaning unit and the cleaned gas is returned to the pipeline at the second point.
In a preferred embodiment of the method according to the invention, the cleaning unit is provided, close to its first connection point. with an inlet for purging gas, and purging gas is supplied to the cleaning unit during the cleaning process.
The present invention further provides a cleaning unit for use in the pipeline cleaning method according to the invention, characterised in that the cleaning unit comprises, connected in series, first means for connecting the cleaning unit to the pipeline, first valve means, one or more separation stages for mechanical separation of debris from the gas/debris mixture, a blower for creating suction, second valve means connected in parallel with the blower, third valve means. a non-return valve, and second means for connecting the cleaning unit to the pipeline.
The cleaning unit according to the present invention preferably further comprises a plurality of sensors for measuring the pressure at a plurality of points in the cleaning unit, and control system for registering the output of the sensors, determining whether a hazard condition exists and taking appropriate action.
The control system is preferably designed to indicate where in the cleaning system, a hazard condition has originated. The control system is particularly preferably adapted to allow the cleaning system only to operate within pre-set system parameters.
The present invention further provides a trailer unit which comprises a cleaning unit mounted on a trailer, within a housing.